This invention relates to polyisocyanate derived adducts, to emulsifiable polyisocyanates which employ those adducts, and to emulsions which include the emulsifiable polyisocyanates.
The use of water based coatings is important due to environmental considerations. In the case of isocyanate-reactive coatings, however, water presents a problem in that the isocyanate groups react with water. In order to overcome this disadvantage, the prior art has used emulsifiable adducts which are the reaction products of polyisocyanates and hydroxy functional polyethers. These adducts have latent isocyanate functionality to assist in crosslinking of the water based coating and sufficient hydrophilic character to keep the water based coating composition dispersed in an aqueous medium. These adducts, however, tend to react with water to form urea reaction products which reduce the working life of the emulsifiable polyisocyanate. Moreover, exposure of these emulsifiable polyisocyanates to heat can form undesirable polyureas which greatly reduces the pot life of the emulsifiable polyisocyanate.
A need exists for more stable water emulsifiable polyisocyanates which are less likely to react with water to extend the working life of the emulsifiable polyisocyanates in water.
In a first aspect, the invention relates to polyisocyanate derived adducts. The adducts are the reaction products of a urethane prepolymer and a capping agent. The capping agent is any of methoxypolyoxyethylene monols, polyoxyethylene-polyoxypropylene monols, and mixtures thereof. The urethane prepolymer is the reaction product of a dihydroxy functional polyol and an isocyanate. The dihydroxy functional polyol is any of polyoxyethylene glycol and polyoxyethylene polyoxypropylene glycols. Preferably, the methoxypolyoxyethylene monols have a molecular weight of about 350 to about 750, and the polyoxyethylene-polyoxypropylene monols have a molecular weight of about 270 to about 3930. Preferably, the urethane prepolymer and the capping agent are present in a weight ratio of urethane prepolymer to capping agent of about 2:1 to about 1:2, the dihydroxy functional polyol and the isocyanate are present in a weight ratio of dihydroxy functional polyol to isocyanate of about 2:1 to about 25:1, and the capping agent and the urethane prepolymer are present in a weight ratio of the capping agent to the prepolymer of about 1:1 to about 1:3.
In another aspect, the invention relates to an emulsifiable polyisocyanate that includes an isocyanate and a polyisocyanate derived adduct.
In yet another aspect, the invention relates to an aqueous emulsion having greatly improved stability. The aqueous emulsion includes emulsifiable polyisocyanate. The emulsifiable polyisocyanate includes an isocyanate and a polyisocyanate derived adduct. The polyisocyanate derived adduct includes the reaction product of a urethane prepolymer and a capping agent. The capping agent may be any of methoxypolyoxyethylene monols, polyoxyethylene-polyoxypropylene monols, and mixtures thereof. The urethane prepolymer is the reaction product of a dihydroxy functional polyol and an isocyanate. The urethane prepolymer and the capping agent can be present in a weight ratio of urethane prepolymer to capping agent of about 2:1 to about 1:2, the dihydroxy functional polyol and the isocyanate can be present in a weight ratio of dihydroxy functional polyol to isocyanate of about 2:1 to about 25:1, and the capping agent and urethane prepolymer are present in a weight ratio of the capping agent to the prepolymer of about 1:1 to about 1:3.
In yet another aspect, the invention relates to an aqueous latex emulsion having greatly increased stability. The aqueous latex emulsion includes an emulsifiable isocyanate. The emulsifiable polyisocyanate may be any of a first reaction product of polymeric methane diphenyl diisocyante, methoxypolyoxyethylene monol, and a polyisocyanate derived adduct, the adduct comprising the reaction product of a urethane prepolymer and a methoxypolyoxyethylene monol, wherein the urethane prepolymer is the reaction product of a dihydroxy functional polyol and an isocyanate, a second reaction product of product of uretomine modified 4,4xe2x80x2-diphenylmethane diisocyanate having about 26% NCO, and a mixture of methoxypolyoxyethylene monol and a polyisocyanate derived adduct comprising the reaction product of a urethane prepolymer and a methoxypolyoxyethylene monol, wherein the urethane prepolymer is the reaction product of a dihydroxy functional polyol and an isocyanate, and a third reaction product of uretonimine modified 4,4xe2x80x2-diphenylmethane diisocyanate having a NCO value of about 29.3%, and a mixture of methoxypolyoxyethylene monol and a polyisocyanate derived adduct comprising the reaction product of a urethane prepolymer and a methoxypolyoxyethylene monol, wherein the urethane prepolymer is the reaction product of a dihydroxy functional polyol and an isocyanate.
Having summarized the invention, the invention is described in detail below by reference to the detailed description below and the following non-limiting examples.
Glossary of Terms and Definitions:
1. Arcol PPG-725 is a polyoxypropylene glycol of the formula HOxe2x80x94(CH2CH3CHO)nxe2x80x94H from Lyondell Chemical Company and has a molecular weight of 725.
2. Carbowax MPEG 350 is a methoxypolyoxyethylene monol of the formula CH3xe2x80x94(OCH2CH2)nxe2x80x94OH where n has an average number of 7. Carbowax 350 is available from Union Carbide Chemicals and Plastics and has a molecular weight of 350.
3. Carbowax 550 is a methoxypolyoxyethylene monol of the formula CH3xe2x80x94(OCH2CH2)nxe2x80x940H where n has an average number of 12. Carbowax 550 is available from Union Carbide Chemicals and Plastics and has a molecular weight of 550.
4. Carbowax 750 is a methoxypolyoxyethylene monol of the formula CH3xe2x80x94(OCH2CH2)nxe2x80x94OH where n has an average number of 16. Carbowax 750 is available from Union Carbide Chemicals and Plastics and has a molecular weight of 750.
5. Carbowax 600 is a polyoxyethylene glycol of the formula Hxe2x80x94(OCH2CH2)nxe2x80x94OH where n is an average number of 13. Carbowax 600 is available from Union Carbide Chemicals and plastics and has a molecular weight of 600.
6. Castor oil is a trifunctional, low molecular weight fatty ester polyol that has a hydroxyl No. 164.
7. Ucon 50-HB-55 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethylene and oxypropylene groups. Ucon 50-HB-55 is available from Union Carbide Chemicals and plastics and has a molecular weight of 270.
8. Ucon 50-HB-100 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethylene and oxypropylene groups. Ucon 50-HB-100 is available from Union Carbide Chemicals and plastics and has a molecular weight of 520.
9. Ucon 50-HB-170 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethylene and oxypropylene groups. Ucon 50-HB-100 is available from Union Carbide Chemicals and plastics and has a molecular weight of 750.
10. Ucon 50-HB-260 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethylene and oxypropylene groups. Ucon 50-HB-260 is available from Union Carbide Chemicals and plastics and has a molecular weight of 970.
11. Ucon 50-HB-400 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethylene and oxypropylene groups. Ucon 50-HB-400 is available from Union Carbide Chemicals and plastics and has a molecular weight of 1230.
12. Ucon 50-HB-660 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethylene and oxypropylene groups. Ucon 50-HB-660 is available from Union Carbide Chemicals and plastics and has a molecular weight of 1590.
13. Ucon 50-HB-2000 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethyl and oxypropylene groups. Ucon 50-HB-2000 is available from Union Carbide Chemicals and plastics and has a molecular weight of 2660.
14. Ucon 50-HB-3520 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethlene and oxypropylene groups. Ucon 50-HB-3520 is available from Union Carbide Chemicals and plastics and has a molecular weight of 3380.
15. Ucon 50-HB-5100 is an alcohol started polyoxyethylene polyoxypropylene monol of the formula ROxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has equal amounts by weight of oxyethylene and oxypropylene groups. Ucon 50-HB-5100 is available from Union Carbide Chemicals and plastics and has a molecular weight of 3930.
16. Ucon 75-H-450 is a polyoxyethylene-polyoxypropylene glycol of the formula HOxe2x80x94(CH2CH3CHO)mxe2x80x94(CH2CH2O)nxe2x80x94H and has 75 weight percent of oxyethylene and 25 weight percent oxypropylene groups. Ucon 75-H-450 is available from Union Carbide Chemicals and plastics and has a molecular weight of 980.
17. Ucon 75-H-1400 is a polyoxyethylene polyoxypropylene glycol of the formula HOxe2x80x94(CH2CH3CHO)nxe2x80x94(CH2CH2O)nxe2x80x94H and has 75 weight percent of oxyethylene and 25 weight percent oxypropylene groups. Ucon 75-H-1400 is available from Union Carbide Chemicals and plastics and has a molecular weight of 2500.
18.Rubinate 44 is 4,4xe2x80x2-diphenylmethane diisocyanate that has a % NCO value of 33.5 and a functionality of 2.0 from Huntsman Polyurethanes.
19. Rubinate 1670 is uretonimine modified 4,4xe2x80x2-diphenylmethane diisocyanate that has a % NCO value of 26 and a functionality of 2.05 from Huntsman Polyurethanes.
20. Rubinate 1680 is uretonimine modified 4,4xe2x80x2-diphenylmethane diisocyanate that has a % NCO value of 29.3 and a functionality of 2.1 from Huntsman Polyurethanes.
21. Rubinate 9236 is modified diphenylmethane diisocyanate based on Rubinate M that has a % NCO value of 30.1 and a functionality of 2.7 from Huntsman Polyurethanes.
22. Rubinate M is polymeric methane diphenyl diisocyante that has an isocyanate value of 31.5% and a functionality of 2.7 from Huntsman Polyurethanes.
23. Latex Dur-o-set E-250 is an ethylene vinyl acetate copolymer aqueous emulsion from National Starch and Chemical Company, Bridgewater, N.J. Dur-o-set E-250 has a solids content of 56%, a pH of 4.7, and a density of 4.7 lbs./gal.
24. Desmodur XO-672 is MDI prepolymer from Bayer Corp.
All molecular weights, unless otherwise specified, are number average.
Isocyanates
Suitable isocyanates which may be employed in the invention for making the polyisocyanate derived adducts of the present invention include known aliphatic, cycloaliphatic, aromatic and heterocyclic polyisocyanates. Also suitable are polyisocyanates which contain carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, biuret groups, and urea groups.
Examples of aromatic isocyanates which may be employed include but are not limited to 2,4-hexahydrotoluene diisocyanate, 2,6-hexahydrotoluene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluene diisocyanate (TDI), 2,6-toluene diisocyanate, diphenyl methane-2,4xe2x80x2-diisocyanate(2,4xe2x80x2MDI), diphenyl methane-4,4xe2x80x2-diisocyanate (4,4xe2x80x2MDI), naphthalene-1,5-diisocyanate. triphenyl methane-4,4xe2x80x2,4xe2x80x3-triisocyanate, polymethylene polyphenylene polyisocyanates and mixtures thereof.
Examples of aliphatic polyisocyanates which may be employed include but are not limited to ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2,4,4-tri-methyl-1,6-hexamethylene diisocyanate, and 1,12-dodecane diisocyanate.
Examples of cycloaliphatic polyisocyanates which may be employed include but are not limited to cyclohexane-1,4-diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (isophorone diisocyanate or IPDI), 2,4xe2x80x2-dicyclohexylmethane diisocyanate, 4,4xe2x80x2-dicyclohexylmethane diisocyanate.
Preferred isocyanates include ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2,4,4-tri-methyl-1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (isophorone diisocyanate or IPDI), 2,4-hexahydrotoluene diisocyanate, 2,6-hexahydrotoluene diisocyanate, 2,4xe2x80x2-dicyclohexylhexylmethane diisocyanate, 4,4xe2x80x2-dicyclohexylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-toluene diisocyanate (TDI), 2,6-toluene diisocyanate, diphenyl methane-2,4xe2x80x2-diisocyanate, diphenyl methane-4,4xe2x80x3-diisocyanate (MDI), naphthalene-1,5-diisocyanate, triphenyl methane-4,4xe2x80x2,4xe2x80x3-triisocyanate, polymethylene polyphenylene polyisocyanates and mixtures thereof. A particularly preferred polyisocyanate for making the polyisocyanate derived adducts of the present invention is 4,4xe2x80x2 diphenyl methane diisocyanate (4,4xe2x80x2MDI).
Hydroxy Functional Monols and Polyols
Hydroxy functional monols and polyols which may be employed in the invention include mono-hydroxy functional polyoxyethylene monols, dihydroxy functional polyoxyethylene glycols, mono-hydroxyfunctional polyoxyethylene-polyoxypropylene monol, and dihydroxy functional EO/PO glycols. Preferably, the mono-hydroxy functional polyoxyethylene monol and the monohydroxy functional EO/PO monols are those available under the tradenames Carbowax MPEG and UCON, respectively, from Union Carbide.
Carbowax MPEG mono-hydroxy functional polyoxyethylene monols have an all ethylene oxide (EO) backbone and a molecular weight of about 100 to about 5000. The Carbowax MPEGs used in the invention preferably have a molecular weight of from about 300 to about 800. The Ucon monohydroxy functional EO/PO glycols have a molecular weight of from about 270 to about 3930.
The dihydroxy functional polyoxyethylene glycols and the dihydroxy functional EO/PO glycols preferably are those available under the tradenames Carbowax PEG and Ucon, respectively, from Union Carbide. The Carbowax dihydroxy polyoxyethylene glycols employed in the invention have a molecular weight of about 500 to about 2500, preferably about 600 to about 800. The Ucon dihydroxy functional EO/PO glycols employed in the invention have a molecular weight of about 500 to about 5000, preferably about 980 to about 2500.
Preparation of Polyisocyanate Derived Adducts
The polyisocyanate derived adducts of the invention can be prepared by conventional polymerization techniques, either batch-wise by combining all of the ingredients, or step-wise. One or more of the aforementioned polyols are reacted with isocyanate to produce an adduct. The adduct can be made according to two different embodiments. The number average molecular weight of the polyisocyanate derived adducts of the invention are from about 600 to about 11000 as determined by gel permeation chromatography.
The first embodiment entails a single step procedure wherein a mono-hydroxy functional monol is reacted with a polyisocyanate to produce the adduct. The total amount of monol added is a stoichiometric equivalent or more with respect to the polyisocyanate. Preferably, the polyols are Carbowax MPEG and Ucon polyols, alone or in combination. The amount of polyol added is sufficient to consume about 99%, preferably 100% of the isocyanate functionality so as to not leave any isocyanate reactive functionality in the resulting polyisocyanate derived adduct.
The alchol(s) are added at a controlled rate to the polyisocyanate in order to maintain the reaction temperature between about 50xc2x0 C. to about 100xc2x0 C., preferably about 70xc2x0 C. to about 80xc2x0 C., most preferably below about 85xc2x0 C. The total amount of monol added to the polyisocyanate is from about 0.95 of an equivalent per equivalent of polyisocyanate, preferably from about 0.99 to 1.03 of monol to polyisocyanate equivalent.
The reaction is monitored by isocyanate absorbance band by using a Fourier transform infrared spectrometer and isocyanate titration. The reaction end point is achieved when no isocyanate functionality remains in the resulting polyisocyanate derived adduct.
The second embodiment for manufacture of the polyisocyanate derived adducts of the invention entails a two step procedure. Step one entails reacting a di-hydroxy functional polyol with polyisocyanate to make a polyisocyanate terminated intermediate at a reaction temperature of about 70xc2x0 C. to about 80xc2x0 C. The amount of di-hydroxy functional polyol reacted with the polyisocyanate is less than one stoichiometric equivalent with respect to the polyisocyanate. The amount of polyol reacted with the polyisocyanate is preferably not less than about 0.85 of an equivalent per equivalent of isocyanate, more preferably from about 0.90 to 0.97 of polyol to isocyanate equivalent. In step two, a mono-hydroxy functional alchol is reacted with the polyisocyanate terminated intermediate made in the first step. The amount of mono-hydroxy functional monol employed is sufficient to consume about 99%, preferably 100% of the isocyanate functionality without leaving any of the remaining isocyanate reactive functionality in the resulting polyisocyanate derived adduct.
Reaction of the mono-hydroxy functional monol with the isocyanate terminated intermediate is monitored by isocyanate absorbance band by using a Fourier transform infrared spectrometer and isocyanate titration. The reaction end point is achieved when no isocyanate functionality remains in the resulting polyisocyanate derived adduct.
Although, in principle, it is intended that all of the isocyanate functionality of the polyisocyanate be reacted, it should be understood that 100 percent complete reaction cannot always be attained, and therefore, trace amounts of unreacted isocyanate and/or unreacted hydroxyls should not be considered as outside the scope of the invention. Alternatively, reacting xe2x80x9callxe2x80x9d of the isocyanate for the purposes of the present invention may be defined as at least 99 percent complete reaction, preferably 100 percent.
The polyisocyanate derived adducts of the invention, through selection of the mono-hydroxy functional monol as taught herein below, can be tailored to have a desired hydrophilicity. Generally, these adducts are about 30%, preferably about 40%, most preferably about 100 percent soluble in water at room temperature.
The mono-hydroxy functional monol can be mono-hydroxy functional polyoxyethylene monol or mono-hydroxy functional polyoxyethylene/polyoxypropylene monol. The blend may have about 5 to 1 ratio by weight of polyisocyanate derived adduct to mono-hydroxy functional monol, preferably about 2.5 to 1 ratio by weight, most preferably about 1 to 1 ratio by weight.
Preparation of Emulsifiable Polyisocyanates from the Polyisocyanate Derived Adducts
Emulsifiable polyisocyanates are prepared by blending and agitation of a polyisocyanate and a polyisocyanate derived adduct until a homogeneous solution of the polyisocyanate derived adduct in the isocyanate is attained. The solution of polyisocyanate derived adduct in isocyanate may have about 1 to about 25 percent by weight of the polyisocyanate derived adduct, preferably about 1 to about 15 percent, most preferably about 2 to about 10 percent, based on the combined weight of the adduct and free isocyanate, remainder polyisocyanate.
Preparation of Aqueous Emulsions of Emulsifiable Polyisocyanates Containing Polyisocyanate Derived Adducts
Aqueous emulsions of emulsifiable polyisocyanates are prepared by blending the emulsifiable polyisocyanate containing derived adduct with water at a 1:1 ratio by weight under vigorous agitation until the isocyanate is visibly completely emulsified, as indicated by a uniformly cloudy liquid. The stability (potlife) of the resulting aqueous emulsion is measured by changes in viscosity of the liquid vs. time. Viscosities are measured every 30-60 minutes using a Brookfield viscometer. The potlife of the emulsion is defined as the time when the change in the difference between successive viscosity measurements is more than 100% compared to the immediately preceding viscosity measurement.